I'm selling it because my barrel is shorter than the suggested minimum and I have a non-standard barrel nut, so it just won't cycle suppressed subs for me. Copy-pasted product description is below: Adams Arms 300BLK P Series Adjustable Gas Piston Kit Low Profile .750 Micro Block AR15 AR-15 300 BLACKOUT **NOW AVAILABLE IN NEXT GENERATION 300BLK Blackout SPECIFIC KIT for Pistol Length .300 Gas Systems. INCLUDES A LOW MASS BOLT CARRIER FOR THIS HEAVY LOWER POWDER CALIBER WHICH ACCOUNTS FOR A HIGHER PRICE OVER STANDARD KITS 300BLK Kit features an enlarged drive rod gas cup brought over from Adam's .308 spec kit design and a unique .300 gas block with an enlarged gas channel for improved flow for this low powder caliber. Excellent for subsonics!** THESE P SERIES KITS INCLUDE ADJUSTABLE, CONCEALABLE, GAS BLOCK PISTON CONVERSION KITS AND REPLACE THE EARLIER XLP (P Series is 30% lighter with enhanced locking lugs to better secure the gas plug). Kits are designed to retrofit a direct gas impingement system (i.e. upper with a gas tube) and change it to a clean running, ultra reliable, piston system. Base Kits DO NOT INCLUDE BOLT/FIRING PIN/CAM PIN BUT MAY BE UPGRADED FOR ADDED COST WITH OPTION). UNLESS A BOLT COMPLETION KIT IS ADDED, THE BCG AND RIFLE PICS ARE FOR EXAMPLE ONLY OF COMPLETED BUILDS. Adams Arm's AR-15 conversion kit system is compatible with .300BLK with this appropriate 300 Blackout kit. Kit includes: Patented Lifecoated One-Piece Bolt Carrier P Series .750 Micro Block - Adjustable (5 Settings - 100%/74%/53%/32%/11%) weight 4.1 oz Bolt Spring Drive Rod with Bushing and Spring Installation Instruction Card NOTE: ADAMS HAS DISCONTINUED SENDING RECEIVER BUSHING AND INSTALL TOOL AS THESE WERE DEEMED UNNECESSARY FOR PROPER SUPPORT. The Adams Arms Piston System: A short stroke free floating piston system. Is Self-Cleaning. Carbon and gases are expelled forward, away from operator. Corrosive resistant coating processes. Harmonics are not transferred into the barrel. Doesn't vent directly to atmospheric pressure; this eliminates flash signature and super sonic crack which is optimal for night vision and suppresses fire. Has a Lifetime Warranty. 300BLK (We only recommend a Pistol Gas Length and a Low Mass Carrier for optimal performance) PK-MICRO-ADJ-300BLK FGAA-03300 We recommend using a standard barrel nut or barrel nut with similar measurements for proper fit and function of the kit. Many aftermarket proprietary barrel nuts do not offer the clearance for the drive rod or proper seating of the spring and bushing. Micro Gas Blocks should have the set screws torqued to 87 in-lbs LifeCoat is more than just an application or coating processes. It is the most technologically advanced coating processes, material and machining available on the market today. LifeCoat is the idea that certain processes and materials are superior for their applicable needs and when combined they offer efficiencies unparalleled to anything currently available. NOTE: Due to low powder nature of 300BLK, it is not recommended to use barrels below 8" long due to the further reduction in propellant powder burn for at shorter lengths. 300BLK typically achieves full powder burn at approximately 10.5". We have seen some customers go down to 7.5", but that length takes a bit of tuning for reliable piston cycling (i.e. lighter buffer, recoil spring or gas port hole enlargement). Adams Arms only guarantees reliable cycling of supersonic ammunition on all 8.5" and longer barrels and subsonic ammunition with the use of a suppressor.